In man, there have been many descriptions of diseases where gammadelta T cells may play a role. there have been increased numbers of gammadelta T cells associated with infectious diseases such as tuberculosis, with diseases of autoimmune etiology such as rheumatoid arthritis, and with malignant disease. Many antigens have been described for gammadelta T cells, including mycobacterial proteins, heatshock proteins, staphylococcal endotoxin A (SEA), and a cell surface molecule on Daudi leukemia cells. the long term objective of this proposal is to understand how the gammadelta T cell recognizes antigen, a function that is thought to be performed by the gammadelta T cell receptor (TCR). It has been hypothesized that this receptor will interact with antigen in the same way that the alphabeta T cell receptor interacts with its ligands. For this study, a series of human gammadelta T cell clones has been isolated that recognize tetanus toxin (TTn), possibly in the context of MHC. Some of these clones can also specifically recognize other antigens including the Daudi leukemia cell line. the cDNAs coding for the TCR have been isolated and expressed in a host T cell that does not express an endogenous TCR. This study will use these transfectants to analyze in molecular detail the requirements of the gammadelta TCR to recognize a bacterial protein antigen and apparent superantigens: 1) Establish that specificity for tetanus and for superantigens can be transferred by the adoptive receptor. The transfectants will be stimulated with antigen, and the IL-2 response will be measured. Controls will include alphabeta transfectants specific for TTn and gammadelta transfectants from non-responding cells. 2) Determine the epitopes of tetanus toxin that are recognized by gammadelta TCR. By comparing the response to antigen on fixed versus unfixed antigen presenting cells, the need for antigen processing of TTn will be determined. If gammadelta receptors recognize TTn as a peptide, a series of TTn peptides produced in bacteria will be tested to find a minimal antigen recognized by the receptor. 3. Determine the functional requirements of the CDR of the gammadelta TCR for antigen recognition of tetanus toxin. Models of the alphabeta TCR based on homology with immunoglobulin structures have led to the proposal that CDR1 (CDR- complementarity determining region) and CDR2 recognize MHC while CDR3 recognizes peptide. The model predicts that antigen specificity can be transferred by transferring the CDRs from one receptor to another. Mutations of this type will be used to test the hypothesis on the gammadelta TCR. 4) Establish the regions of the gammadelta receptor that are necessary for binding antigens that appear to be recognized as superantigens. Superantigens can be recognized by alphabeta TCR in a way different from the recognition of peptides. the regions of the gammadelta TCR that are responsible for the recognition of apparent superantigens will be determined with adoptive receptors that have selective mutations. These studies on the recognition properties of the gammadelta T cell receptor will clarify how the gammadelta T cell recognizes antigen and will provide a system where disease associated gammadelta T cells and antigens can be studied in the future.